Understanding the water use characteristics of coexisting plants is essential for revegetation and the sustainable management of water resources. However, the water sources used by coexisting plants in rock-dominated habitats are currently much less clear than in homogeneous soils. We investigated the water use characteristics of six coexisting species in a subtropical karst desertification area using stable isotopes (S2H, S18O, and S13C). The results showed that the six coexisting plants flexibly switched water sources between dry and rainy seasons according to soil moisture conditions, but there was no significant difference in water uptake plasticity among the species (p > 0.05). During the study period, shallow fissure soil water was the dominant water source for all species (43.40 %-51.76 %), while the dependence on groundwater was the lowest (5.81 %-13.95 %). In addition, the shallow water sources (topsoil water and shallow fissure soil water) were more relied upon by the shrub species than the tree species. The ecological niche overlap indices among coexisting species were relatively high (0.68-0.98), which implied that there is intense water competition among these coexisting species. Plant leaf S13C also had obvious seasonal patterns of change, and water use efficiency (WUE) showed that it was higher in the dry season than in the rainy season, with significant differences in the mean values among species (p < 0.05). The WUE of plants was significantly negatively correlated with the relative extractable water (REW) (p < 0.05), while it was significantly positively correlated with the vapor pressure deficit (VPD) (p < 0.05). Differences in water-use efficiency among species account for the coexistence of plants in the absence of hydrological niche segregation (HNS). This study provides new insights into the water use relationships among coexisting plants in rock-dominated habitats, and serves as a reference for restoring vegetation in subtropical karst desertification.